In organic electronic devices such as organic photovoltaics (OPVs), organic light emiting devices (OLEDs), and organic solid state lasers it is common to utilize multi-layer structures. While this is typically a simple process for vacuum-processed films, problems arise for solution-processed films. When multi-layer structures are fabricated from solution-processed films, the underlying layers can be re-dissolved, as orthogonal solvents are uncommon.
Here, the inventors present a method of decreasing the re-dissolution of underlying organic layers by incorporating solvent vapor annealing (SVA). The inventors have devised a compound protection layer scheme to allow solution processing of multi-layer organic film structures. The process scheme is useful where orthogonal solvents are not available. The process scheme can be useful for such technologies as fabrication of OPVs and OLEDs as examples.
The inventors have verified the compound protection scheme by fabricating a stacked OPV device structure. The first solution processed layer is coated with a layer, in this case a fullerene, that is insoluble in the solvent used in depositing the second solution processed layer. By SVA the first layer after the deposition of the fullerne, the first solution processed layer becomes densified. Next, a very thin metal oxide layer is deposited completing the compound protection layer of fullerene+metal oxide. Then, on deposition of the second solution processed layer using a solvent (trimethylformamine) that is less effective in redissolving the first layer (functionalized squaraines) than its original solvent (chloroform) that have since been SVA, the first layer is undamaged and high performance stacked OPV cells result.
Optoelectronic devices rely on the optical and electronic properties of materials to either produce or detect electromagnetic radiation electronically or to generate electricity from ambient electromagnetic radiation.
Photosensitive optoelectronic devices convert electromagnetic radiation into an electrical signal or electricity. Solar cells, also called photovoltaic (“PV”) devices, are a type of photosensitive optoelectronic device that is specifically used to generate electrical power. Photoconductor cells are a type of photosensitive optoelectronic device that are used in conjunction with signal detection circuitry which monitors the resistance of the device to detect changes due to absorbed light. Photodetectors, which may receive an applied bias voltage, are a type of photosensitive optoelectronic device that are used in conjunction with current detecting circuits which measures the current generated when the photodetector is exposed to electromagnetic radiation.
These three classes of photosensitive optoelectronic devices may be distinguished according to whether a rectifying junction as defined below is present and also according to whether the device is operated with an external applied voltage, also known as a bias or bias voltage. A photoconductor cell does not have a rectifying junction and is normally operated with a bias. A PV device has at least one rectifying junction and is operated with no bias. A photodetector has at least one rectifying junction and is usually but not always operated with a bias.
As used herein, the term “rectifying” denotes, inter alia, that an interface has an asymmetric conduction characteristic, i.e., the interface supports electronic charge transport preferably in one direction. The term “semiconductor” denotes materials which can conduct electricity when charge carriers are induced by thermal or electromagnetic excitation. The term “photoconductive” generally relates to the process in which electromagnetic radiant energy is absorbed and thereby converted to excitation energy of electric charge carriers so that the carriers can conduct (i.e., transport) electric charge in a material. The term “photoconductive material” refers to semiconductor materials which are utilized for their property of absorbing electromagnetic radiation to generate electric charge carriers. As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as being “on” or “over” a second layer, there may be intervening layers, unless it is specified that the first layer is “in physical contact with” the second layer.